1. Field
Exemplary embodiments of the present invention relate to a method for fabricating a semiconductor device, and more particularly, to a hydrogen treatment method for improving refresh characteristics.
2. Description of the Related Art
With high integration of semiconductor devices, it has been difficult to secure a refresh time of a dynamic random-access memory (DRAM) cell transistor. In order to secure a refresh time, hydrogen treatment is performed on a semiconductor substrate. The hydrogen treatment is performed to improve an electric connection characteristic between metal interconnections or between the semiconductor substrate and metal interconnections, enhance the characteristic and reliability of a semiconductor device, and increase productivity during a fabrication process.
In the case of a DRAM, an interface state, formed by a dangling bond of silicon, may exist between a silicon oxide layer (for example, isolation layer or gate dielectric layer) and a semiconductor substrate. Through the interface state, a leakage current may flow from a diffusion layer to the substrate, thereby degrading a hold characteristic of DRAM. Furthermore, a transistor characteristic such as a threshold voltage or current voltage characteristic may vary, thereby making it difficult to fabricate a reliable semiconductor device.
The hydrogen treatment supplies hydrogen to the interface, and the supplied hydrogen eliminates the dangling bond, thereby reducing the interface state. However, with the continuous integration and high density of semiconductor devices, it is becoming difficult to sufficiently diffuse hydrogen to a target interface through the hydrogen treatment. Therefore, it becomes necessary to perform the hydrogen treatment at a higher temperature or for a longer processing time.
However, if the processing time is lengthened, productivity may decrease. Furthermore, when the hydrogen treatment is performed at an excessively high temperature, spikes or hillocks may be formed on metal interconnections, thereby reducing the reliability of the DRAM.
During the hydrogen treatment, a hydrogen diffusion path is formed from an edge of a wafer. This is because a nitride layer, having low diffusivity of hydrogen, is formed on portions of the wafer. In particular, a silicon nitride layer is very densely formed by a low pressure chemical vapor deposition (LPCVD method, and may be used as a diffusion barrier for hydrogen.
Because of a nitride layer formed on a front side of the wafer, permeation and diffusion of hydrogen are not directly performed, but rather, are performed from the edge of the wafer, where the nitride layer is not formed. Accordingly, since hydrogen passivation is not sufficiently performed toward the center of the wafer, the refresh time may be degraded.
Such a problem is discovered in all processes, and becomes more serious under a situation in which it becomes difficult to secure the refresh time, with the miniaturization of devices.